During an interview Sunday with CNN "State of the Union" host Gloria Borger, he cautioned shoppers who plan to visit the mall that Al-Shabaab included on a list of targets in a video released this weekend.

"If anyone is planning to go to the Mall of America today, they've got to be particularly careful," Johnson said. "There will be enhanced security there, but public vigilance, public awareness and public caution in situations like this is particularly important, and it's the environment we're in, frankly."

His comments come as the Mall of America implements new security measures -- some of which the mall said in a statement would be noticeable to shoppers.

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Johnson cautions on Mall of America threat

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Another DHS official clarified Johnson's remarks later in the morning.

"Sec. Johnson didn't say that they should not go to the mall, he told shoppers to be extra vigilant and that security was increased," said DHS assistant secretary Tanya Bradsher.

A law enforcement official, also reacting to Johnson's remarks, said there's no indication of an actual threat against any malls in the U.S.

"No one should avoid going to the mall because of this random online threat," the official said. "The FBI has a program to work with various malls around the country to improve security."

Al-Shabaab has heavily targeted the Minneapolis area, home to the largest Somali population in the United States, for recruiting. The United States killed the group's leader in an air strike in Somalia last year, leading Al-Shabaab to vow to avenge his death.

In the propaganda video released Saturday, the group also discussed its September 2013 attack on a mall in Kenya, which left more than 60 people dead.

Johnson said Al-Shabaab's threats against the Mall of America as well as major malls in Canada and the United Kingdom come as anti-terror officials focus increasingly on stopping "independent efforts in their homelands."

He said Al-Shabaab and other groups like al Qaeda and ISIS compete for new recruits and target Western nationals.

"These groups are relying more and more on independent actors to become inspired, drawn to the cause ... on their own, through their effective use of the Internet," Johnson said. "That's why it's critical that we work in the communities where these folks might be able to recruit to develop a counter-narrative."

Johnson also said the latest threats highlight the "reason why I need a budget."

The Department of Homeland Security is just days away from seeing its funding expire, which Johnson said would trigger about 30,000 furloughs -- including 80% the Federal Emergency Management Agency's workers.

"It's absurd that we're even having this conversation about Congress's inability to fund Homeland Security in these challenging times," Johnson said.

Congress is mired in a fight over the department's funding, as majority Republicans insist any bill to pay for its operations must also include provisions that roll back President Barack Obama's executive actions on immigration -- and Democrats insist they won't support such a measure.

Because Democrats hold enough seats to keep the Senate from crossing its 60-vote procedural threshold, a House-passed bill hasn't advanced there, and Republicans in the House and Senate don't appear to have agreed on a way forward.

"The thing that, frankly, is frustrating to me -- when I go to the Senate, they say, 'It's not us, it's the House, go over to the House side and talk to them,'" Johnson said. "I go to the House and they say, 'We passed our bill, it's the Senate.'"